1. Field of the Invention
The present invention relates to a system for recirculating and warming fuel and, more particularly, to a system for providing increased protection against the adverse effects of cold weather on fuel circulation systems, such as those used in connection with diesel engines.
2. Description of Related Art
Some fuels are adversely affected by extreme weather conditions. For example, diesel fuel may tend to thicken, or wax, at cold temperatures. In particular, paraffin wax and other materials may crystallize and precipitate from the fuel to form solids. These solids can build up and clog fuel lines, fuel filters and the like.
In many diesel engines, fuel is withdrawn from one or more fuel tanks and pumped through a supply line to the engine. The fuel needed for combustion is injected into the engine and the excess is returned through a return line to the fuel tank. Once the engine starts, the fuel is warmed as it passes through or in close proximity with the engine and the fuel in the return line is often at a higher temperature than the fuel in the supply line. As a result, waxing and the associated clogging and build-up problems are often more likely to occur in the supply line and other components which encounter the fuel as it is supplied from the tank than in components which encounter the fuel as it returns to the tank.
The return of warmed fuel to the fuel tank may, in some cases, help reduce problems associated with waxing. However, fuel tanks are typically relatively large in comparison to the amount of warmed return fuel. Thus, the warmed return fuel may have only a small or very slow effect on the temperature of the large volume of fuel within the tank. This is particularly true as many operators prefer to keep fuel tanks relatively full in cold conditions. Moreover, if the vehicle is driven in cold conditions, the cold air flowing around the fuel tanks and fuel lines tends to cool the fuel within, counteracting the warming effect of any warmed return fuel added to the tanks.
Some fuel supply systems attempt to alleviate the problems associated with waxing by circulating engine coolant, warmed by the engine, around fuel system components in an effort to warm them. Such systems, however, require a separate circuit to allow such circulation of the engine coolant. The provision of such a circuit increases the cost and complexity of both the fuel system and the engine cooling system.
Other fuel systems provide a thermostatic valve situated adjacent the engine which diverts a portion of the warmed return fuel back into a point in the supply line adjacent the engine. Thus, warmed fuel is returned immediately to the engine. Such system may help protect pumps, filters and injectors located between the valve and the engine. However, such systems make no provision for that portion of the supply line or other fuel system components located between the fuel tank and the valve. Should this portion of the supply line become clogged due to waxing, there is no way to replenish fuel as it is combusted and, after time, the system will exhaust the supply of recirculating warm fuel.